1. Field of the Invention
The invention relates to high-resilience polyurethane foams and more particularly relates to high-resilience polyurethane foams made from mixed alkylene oxide adducts of alkylene diamines.
2. Other Relevant Products in the Field
Polyurethane foams are the most important seating support materials available today. They are made in the form of slabs, which are cut-to-shape, or they are molded to meet specific needs.
Molded foams are commonly of the "high-resilience" (HR) type, and are characterized by high sag factors and improved hysteresis curves compared to the usual slab foams. Unfortunately, HR foams tend to have a high percentage of closed cells, which causes foams to be "tight" and shrink, and detracts from various physical properties. While the use of so-called "polymer polyols" helps to control cell structures, molded and slab HR foams generally have to be crushed in order to give the foams sufficient "breathability".
Most of the molded HR foams manufactured today go into automotive seating. With the recent advent of "in-frame" molding, foams cannot be crushed easily. It, therefore, has become much more important that foams be inherently "open". Unfortunately, generally, as foams are "opened up" by various techniques, the foams will also "process" more poorly. That is, there will be problems with large cells, poor surfaces, etc.
It has now been discovered that certain polyols can be used in otherwise conventional HR foam formulations to give molded HR foams which exhibit improved resistance to tightness and shrinkage--but without sacrifice of processing characteristics. These polyols are alkylene oxide adducts of alkylene diamines. While other alkylene oxide adduct polyols are known, none have been discovered to give improved openness in high-resilience foams.
U.S. Pat. No. 3,535,307 teaches that high molecular weight polyether block polymers may be prepared by the sequential alkoxylation of a polyfunctional initiator with alkylene epoxide components to provide polyether polyols that can be used in the preparation of polyurethanes with improved properties. Further, U.S. Pat. No. 4,111,865 contains descriptions of polymer polyol compositions useful in polyurethane foams having utility as seat cushions with improved static fatigue and humidity sensitivity properties. The polyols here are polyoxypropylene-polyoxyethylene polyols having critical polyoxypropylene and polyoxyethylene contents, hydroxyl functionalities, hydroxyl numbers and primary hydroxyl group contents. Two initiators used in the examples therein are diethylenetriamine and ethylenediamine. Subsequently, the polymer polyols are made by polymerizing acrylonitrile and styrene in the ethylenediamine polyols. It should be emphasized that the ethylenediamine polyols described in U.S. Pat. No. 4,111,865 are intermediates to the polymer polyol end product which forms the invention therein. It was unrecognized that the ethylenediamine polyols themselves had unique physical properties.